Cytochrome P-448 in animals treated with arylhydrocarbons (AH) differs from cytochrome P-450 in control or phenobarbital (PB) treated animals with respect to several parameters including CO difference spectra, ethyl isocyanide difference spectra, substrate specificity, molecular and immunological properties. During the tenure of this grant the additional properties of the low affinity to halothane, metopirone and CO of the reduced form of AH induced P-448 as compared with control and PB induced P-450 have been explored. Our studies for the next year will concentrate on localizing more precisely the bases for these alterations in biophysical and biochemical properties of the multi-enzyme systems induced by AH and PB. The available methods for resolving these systems and purifying their components will be evaluated and compared with the procedures we have developed for purification of the steroid hydroxylase system of adrenal mitochondria. The methods to be applied for studying the interaction of P-450 with other enzymatic components of the system and with various substrates and ligands will include optical spectrophotometry and electron paramagnetic resonance spectroscopy. The physical and chemical properties of the solubilized systems will be compared with those of the corresponding membrane-bound microsomal systems in order to assess to what extent the observed differences between aryl and non-aryl induced P-450 systems can be attributed to changes in the heme, the protein moiety or the microenvironment of the membrane, the final goal being to determine in what way changes in the P-450 systems induced by polycyclic aromatic hydrocarbons and other xenobiotics are of significance in converting procarcinogens to carcinogens or in their inactivation. An additional goal of this project is to study why AH induction appears to differ from that by drugs such as phenobarbital. These differences will be investigated with reference to the effects of age and nutrition of the animals, and rate of absorption and administration of inducer, on the time course of enzyme induction. BIBLIOGRAPHIC REFERENCES: Schleyer, H., Cooper, D.Y., Rosenthal, O., and Cheung, P. The Heme Protein P-450 from the Adrenal Cortex: Studies of the Role of the Axial Ligands. Biophys. J. 17, 65a (1977).